The present invention relates to an indoor unit for an air conditioner and particularly to a ceiling embedded type indoor unit in which a U-shaped or C-shaped heat exchanger is provided and a blower is provided in an inner space formed by the heat exchanger.
In a ceiling embedded indoor unit having four air outlet ports respectively facing four directions and a plurality of centrifugal blowers arranged side by side, structure is known in which a heat exchanger formed in a rectangle shape or two heat exchangers formed in an L-shape are arranged so as to surround the centrifugal blowers, and the blowers arranged in the same level. However, in a ceiling embedded indoor unit having two air outlet ports facing opposite directions, such structure is not known.
Further, in controlling a number of rotation of a plurality of blowers, an embodiment in which a number of rotation of a certain blower is fixed and a number of rotation of another blower is variable is present in an outdoor unit, however, is not present in an indoor unit.
It is required that a height of the ceiling embedded type (regardless of four directions blowing-out type or two directions blowing-out type) indoor unit for the air conditioner is set to be as small as possible so that the indoor unit can be placed even in a portion in which a depth of the ceiling is small (for example, 300 mm or less). In order to technically limit a height of the indoor unit to a low level, it is a problem how a height of the heat exchanger which is an element of the indoor unit is made small. Since an area of the heat exchanger is naturally reduced as the height of the heat exchanger is reduced, it is necessary to make a length of the heat exchanger longer correspondingly.
Particularly, in the indoor unit having a large capacity of about 10 kW or more, since it is impossible to increase a width of a casing of the indoor unit due to a limitation for execution, a rectangular casing is frequently employed. In the case of using the rectangular type or U-shape heat exchanger in this casing, the heat exchanger becomes necessarily rectangular, so that a wind velocity balance with respect to the heat exchanger is deteriorated if only one centrifugal blower of which axis is arranged vertically is used. Therefore, a plurality of blowers must be employed.
In this case, in the prior art ceiling embedded indoor unit having four air outlet ports, since the rectangular heat exchanger or the combination of the L-shaped heat exchangers is employed so as to substantially uniformly surround the periphery of the blowers, the wind velocity balance with respect to the heat exchanger becomes substantially uniform even when the numbers of rotation of a plurality of blowers are equal to each other.
However, in the ceiling embedded type two directions blowing-out type indoor unit, in the case of employing the rectangular heat exchanger or the combination of the L-shaped heat exchangers, there are two sides of the heat exchanger which are not positioned at outlet ports, so that it is disadvantageous in view of a cost. Further, in the case of arranging the heat exchanger only in the portion positioned at the outlet ports, two heat exchangers are needed and two refrigerant distributing devices are required. This is disadvantageous in view of a cost.
Accordingly, in the two directions blowing-out type indoor unit, a U-shaped heat exchanger is most suitable in view of a cost. However, in the case of using a plurality of blowers as mentioned above, since the areas of the heat exchanger to which an air discharged from each of the blowers applies are different from each other, the wind velocity balance with respect to the heat exchanger is not uniform. As a result, a problem is expected that an air conditioning capacity is deteriorated and a wind sound is increased.
Further, when the plurality of blowers are operated at the numbers of rotation close to each other, frequency band areas which generate high noise become close to each other. Therefore, a problem also is expected that a beat sound is likely to occur.
Further, when an interval between an inner peripheral surface of the heat exchanger and an outer peripheral surface of an impeller becomes small in order to make the air conditioner compact, an air current at a high velocity blown out from the impeller collides with fins of the heat exchanger in a downstream side of a position at which the heat exchanger and the impeller most approach to each other, whereby a wind sound is generated.
An object of the present invention is to provide a ceiling embedded type indoor unit which can reduce an air passing sound while preventing a beat sound of blowers with setting a wind velocity balance with respect to a heat exchanger uniform and keeping a high air conditioning capacity, in order to restrict a product height and a cost to a low level, even when a plurality of blowers and a U-shaped heat exchanger are used.
Further, another object of the present invention is to provide a ceiling embedded type indoor unit which can secure a long peripheral length of a heat exchanger within a limited space and making a wind velocity with respect to the heat exchanger uniform so as to increase an amount of heat exchange, as a result a compact size can be achieved although the problem as to the cost increase due to employing a plurality of heat exchangers cannot be solved.
Other object of the present invention is to provide an air conditioner preferable for making compact and reducing noise.
In this case, the present invention solves at least one of the problems mentioned above.
In order to achieve the objects mentioned above, in accordance with a first aspect of the present invention, there is provided a ceiling embedded type indoor unit comprising: a casing embedded in a ceiling; a U-shaped heat exchanger placed within the casing, constituted by two side portions and a bottom portion connecting these side portions in one end side, and the side portions and the bottom portion being arranged in a horizontal direction; a plurality of blowers arranged side by side from the bottom portion of the U-shaped heat exchanger to an open end side of the U-shaped heat exchanger in an inner space of the heat exchanger; a plurality of motors of which upper ends are fixed to ceiling side of the casing, the blowers being mounted on rotary shafts provided at the lower ends of the motors; a decorative panel mounted on a lower surface of the casing and having two long air outlet ports in correspondence to the side portions of the U-shaped heat exchanger and an air suction port formed between the air outlet ports; and a control apparatus placed within the casing, wherein the control apparatus controls so that the number of rotation of the blower near a valley portion of the U-shaped heat exchanger becomes high and the number of rotation of the blower near the open end of the U-shaped heat exchanger becomes low. With this control, the wind velocity balance with respect to the U-shaped heat exchanger can be close to a uniform value.
Further, in accordance with a second aspect of the present invention, a ceiling embedded type indoor unit is structured such that a control apparatus controls a number of rotation of the blower close to the open end of the U-shaped heat exchanger to be fixed, controls a number of rotation of the blower close to the valley portion of the U-shaped heat exchanger to be variable, and controls a maximum number of rotation of the blower close to the valley portion of the U-shaped heat exchanger to be higher than the fixed number of rotation of the blower close to the open end of the U-shaped heat exchanger. Since these control circuits are expensive, it is possible to reduce a capacity of the control apparatus by fixing the number of rotation of a certain blower, so that the cost can be reduced.
In the ceiling embedded type indoor unit in accordance with the second aspect, in the case of operating the blower having a variable number of rotation near a wind amount 0 at the lowest wind amount, it is preferable that the control apparatus is structured such as to operate the blower having the variable number of rotation at a number of rotation capable of preventing the discharged air from the blower of the fixed number of rotation from short-circuiting. Further, in order to accurately detect a suction air temperature, it is preferable to place a suction air temperature sensor near the blower having the fixed number of rotation.
Further, in accordance with a third aspect of the present invention, a control apparatus of a ceiling embedded type indoor unit is structured such as to variably control a number of rotation of the blower close to the valley portion of the U-shaped heat exchanger to be higher, controls a number of rotation of the blower close to the open end of the U-shaped heat exchanger to be lower, and controls a ratio between the numbers of rotation of both of the blowers to be fixed. Due to the control mentioned above, it is possible to make the wind velocity balance with respect to the heat exchanger nearly uniform even in the case of switching a wind amount among a sudden wind, a strong wind, a weak wind and the like.
In the ceiling embedded type indoor unit in accordance with the third aspect, in order to accurately detect a suction air temperature, it is preferable to place a suction air temperature sensor near the blower having the high number of rotation.
Further, in the ceiling embedded type indoor unit mentioned above, it is preferable to be structured such that an outlet air temperature sensor is provided, the control apparatus stores an outlet air temperature previously determined on the basis a number of rotation in each of the blowers, a suction air temperature and temperatures of a gas refrigerant and a liquid refrigerant which flow into and out of the heat exchanger, as data, calculates the outlet air temperature on the basis of detected values of the number of rotation in each of the blowers, the suction air temperature, the gas refrigerant temperature and the liquid refrigerant temperature with reference to the data, and outputs the outlet air temperature to the outlet air temperature sensor. Accordingly, even when the wind amount is changed, the outlet air temperature sensor indicates a value close to an average temperature of a whole of the outlet port.
Further, in accordance with a fourth aspect of the present invention, the ceiling embedded type indoor unit is characterized in that positions of a plurality of blowers are vertically shifted. Accordingly, an interference of the air discharged from the adjacent blowers is reduced.
In accordance with a fifth aspect of the present invention, the ceiling embedded type indoor unit is structured such that the heat exchangers are constituted by C-shaped heat exchangers which surround most of peripheries of the blowers. By making the structure in the manner mentioned above, it is possible to set a peripheral length of the heat exchanger long and make a wind velocity distribution nearly uniform.
Further, in accordance with the present invention, it is desirable that the heat exchanger mentioned above is structured such that rectifying plates which protrude inward from an inner peripheral surface of the heat exchanger so as to correspond to at least a height of outlets of the impellers are provided in downward side of the air flow discharged from the impellers at positions at which the inner peripheral surfaces of the heat exchangers and outer peripheral surfaces of the impellers are in the closest vicinity to each other.